Prolactin is an essential hormone for reproduction in mammals. The neuroendocrine mechanisms which govern the secretion of prolactin are only partially understood. Prolactin releasing factors (PRF's) and release-inhibiting factors (PIF's) are secreted by the hypothalamus into hypophyseal portal blood and act directly at the pituitary level to control the rate of prolactin release. In addition, there are a number of brain neuropeptide3s which act, in large part, via indirect mechanisms to induce prolactin secretion. These neuopeptides are present in relatively high concentrations with the hypothalamus of rats and are viewed as potentially important links between the physiologic stimuli which evoke prolactin release and the secretion of PIFs and PRFs into hypophyseal portal blood. the purpose of the proposed study is to determine how neuropeptides stimulate the release of prolactin from the rat pituitary gland, and then to attempt to integrate the prolactin-releasing actions of neuropeptides with those of neurotransmitters. I plan to accomplish these objective first by measuring changes in the secretion rates of hypophysiotropic agents induced by neuropeptide treatment. Having established how each of five neuropeptides affects the secretion of three hypophysiotropic agents, I will then utilize specific blockers of histamine and serotonin action to determine whether these aminergic neurotransmitters mediate the effects of neuropeptides on the secretion of PIF and PRFs into hypophyseal portal blood. The proposed studies will provide valuable informationtoward our understanding of prolactin regulatory processes in particular, and of neuroendocrine integration in general. Moreover, this knowledge can eventually be used for identifying the causes of, and developing treatments for, pathologies of prolactin secretion in humans such as lactationsl insufficiency and galactorrhea-amenorrhea.